Component with a damping filler

ABSTRACT

A method of manufacturing an aerofoil for a gas turbine engine ( 10 ). The method comprises the steps of providing first and second panels ( 16, 18 ), providing a web ( 30 ) between the first and second panels, deforming the panels and the web by applying internal pressure between the panels so as to form a series of internal cavities partitioned by the web. The method further includes the step of either cutting the web ( 30 ) across its entire width or causing the web to fail across its entire width so as to define an aerofoil having first and second panels with at least one protrusion extending from the first panel partially across the space between the first and second panels.

The present invention relates to a component with a damping material asa filler. The invention is particularly, although not exclusively,useful for aerofoils, such as fan blades for a gas turbine engine.

It is known to use hollow aerofoils on gas turbine engines fan blades.The hollow aerofoil is typically formed by inflating a blade pre-cursorat superplastic temperatures and is often provided with an internalmetallic structure to increase strength and prevent so called panting ofthe walls of the aerofoil, ie movement towards and away from each other.To facilitate damping and reduce vibration of the component, the hollowcavity can be filled with a damping material, for example avisco-elastic material. Generally in such filled components, the cavityis smooth walled with no internal structure.

It is an object of the invention to provide an improved component.

According to one aspect of the invention there is provided an aerofoilfor a gas turbine engine comprising first and second panels spaced apartfrom each other, the first panel having at least one protrusionextending therefrom towards the second panel, characterised in that theprotrusion extends partially across the space between the first andsecond panels so as to define a free end of the protrusion and in thatthe free end is surrounded by visco elastic a damping material, and thesecond panel comprises at least one protrusion extending therefromtowards the first panel partially across the space therebetween.

In that way, an internal strengthening structure can be provided and thedamping material is rendered more effective than if it was merelydamping in shear.

Preferably the space between the panels is substantially filled by thedamping material.

A plurality of protrusions may extend from the first panel. In thatcase, the respective free ends of the protrusions are respectivelysurrounded by the damping material and most preferably connectedtogether by means of the damping material.

The second panel comprises at least one protrusion extending therefromtowards the first panel. The protrusion extending from the second panelhas a free end surrounded by damping material. Most preferably, the freeend of the protrusion extending from the second panel and the free endof the protrusion extending from the first panel are connected togetherby means of the damping material.

Where respective protrusions extend from the first and second panels,the protrusions may be co-linear when viewed in section. Alternatively,the protrusions may be offset from each other. Where respectivepluralities of protrusions extend from the first and second panels, theprotrusions extending from the first panel preferably interdentate withthe protrusions extending from the second panel.

Each protrusion may extend for more than half of the distance across thespace between the first and second panels. Alternatively each protrusionmay extend for less than half of the distance across the space betweenthe first and second panels.

The free end of the protrusion may have a cross part extendingtransverse to the rest of the protrusion. The free end may comprise anenlarged head. The free end may comprise a plurality of fins. The freeend may comprise a “U” shaped portion.

The or each protrusion may comprise an elongate rib or vane. The rib mayinclude a bend along the length thereof. Where a plurality ofprotrusions are provided, the protrusions may each comprise an elongaterib and, preferably, at least some of the ribs are not parallel withrespect to each other.

The rib may define a cylinder. Where a plurality of cylinders aredefined by the ribs, the cylinders may be arranged to nest one withinthe other and most preferably the cylinders are arranged concentrically.

The aerofoil is preferably a fan blade. Most preferably, the fan bladeis formed super-plastically and the protrusion comprises a warren girderstructure which is split apart, part of the way between the first andsecond panels of the fan.

According to another aspect of the invention there is provided a methodof manufacturing an aerofoil for a gas turbine engine, the methodcomprising the steps of providing a first panel having at least oneprotrusion extending therefrom, providing a second panel, securing thefirst and second panels together so as to define a space therebetweenand so that the protrusion extends partially across the space betweenthe first and second panels, and injecting a damping material into thespace between the panels so as to surround the free end of theprotrusion.

According to a further aspect of the invention there is provided amethod of manufacturing a component comprising steps of providing firstand second panels, providing a web between the first and second panels,deforming the panels and the web by applying internal pressure betweenthe panels so as to form a series of internal cavities partitioned bythe web, the method being characterised by the steps of either cuttingthe web across its entire width or causing the web to fail across itsentire width so as to define a component having first and second panelswith at least one protrusion extending from the first panel partiallyacross the space between the first and second panels.

It should be noted that this differs from the method in our co-pendingapplication entitled ‘Component with Internal Damping’ due to the factthat the web fails across its entire width or is cut across its entirewidth, whereas the web in the “Component with Internal Damping” case hasapertures formed therethrough.

The method of manufacture preferably comprises the steps of providing aplurality of webs, locally weakening the webs across their entire widthat a position on the webs spaced from the ends thereof, disposing theplurality of webs between two panels, causing the webs to be joined tothe panels, deforming the panels and the webs in two stages, the firststage comprising the steps of heating the panels and the webs to asuperplastic temperature range and applying an internal pressure betweenthe panels so that the panels are pushed apart to contact a die in afirst die position, the second stage comprising the steps of maintainingthe panels and the webs at a hot forming temperature range, below thesuperplastic temperature range and applying an internal pressure betweenthe panels so that the panels are pushed apart to contact a die in asecond die position, whereby the locally weakened parts of the webs failacross the entire width thereof.

FIG. 1 is a perspective view of a blisk comprising a disk and blade bodyfor a gas turbine in accordance with the first aspect of the invention;

FIG. 2 is a cross-section through the blade of FIG. 1 taken on lineII-II in FIG. 1;

FIG. 3 is an enlarged sectional view of part of the blade of FIGS. 1 and2;

FIGS. 4 to 13 are sectional views of various rib formations for use inthe blade of FIGS. 1 and 2;

FIG. 14 is a cross-section through an alternative fan blade inaccordance with the first aspect of the invention and made according tothe method of the third aspect of the invention;

FIGS. 15 a to d show stages in the method of manufacturing the fan bladeshown in FIG. 14 in accordance with the third aspect of the invention;

FIG. 16 is a cross-sectional view of part of a fan blade in accordancewith the invention;

FIG. 17 shows a web membrane for use in the manufacture of the fan ofFIGS. 16, 18 and 19;

FIG. 18 is a cross-sectional view of part of the fan of FIGS. 16 and 17;and

FIGS. 19 a and b are cross-sections through part of the fan of FIG. 16showing two stages in the manufacturing procedure.

In FIG. 1, a blisk 10 comprises a disk 12 and fan blade body 14. Theblade body 14, as best shown in FIGS. 2 and 3, comprises first andsecond panels 16, 18 which are spaced apart to define a void (or cavity)19 therebetween. Each of the first and second panels 16, 18 has a seriesof elongate ribs 20, 22 respectively extending therefrom into the void19. As shown in FIGS. 2 and 3, the ribs 20, 22 extending from theopposing panels are arranged to interdentate.

The void 19 is filled with a visco-elastic damping material 24. By wayof non limiting example, the damping material 24 may be a Huntsman™syntactic damping paste or some such similar product. The dampingmaterial 24 surrounds the ends of the ribs 20, 22 and adheres to theribs and the inner surfaces of the panels. The damping material is ofknown composition and acts to inhibit vibration. Because the ribs 20, 22do not extend across the full width of the void 19 and because they aresurrounded by the visco-elastic material 24 they impart more strain intothe visco-elastic material 24 rather than transmitting load from onepanel 16 to the other 18.

FIG. 1 shows the longitudinal extent of the ribs 20, 22. It can be seenfrom that figure that a preferred configuration of the ribs 20, 22 isfor the ribs near the blade tip to extend substantially parallel withthe blade tip. At the tip, the steady stresses on the panel are less andthe parallel configuration maximises strength of the tip against impact,eg bird strike. The parallel configuration also acts as a dam to preventthe visco-elastic material 24 from overloading and/or escaping the tip.Towards the disk 12, the ribs 20, 22 extend generally parallel with thelongitudinal of the blade body 14 so as to enhance the steady strengthof the blade 10. Some of the ribs 20, 22 have a bend or curve alongtheir length. Other rib configurations are envisaged and could bedesigned to maximise damping from specific mode shapes.

FIGS. 4 to 13 show various rib formations with a variety ofconfigurations of visco-elastic material 24.

In FIG. 4, the ribs 20, 22 only protrude around a quarter of the wayacross the void 19 between the panels. The visco-elastic material 24 inthe FIG. 4 embodiment lies along the inner surface of the panels 16, 18over the ribs 20, 22 with a space between opposite panels 16,18. Herethe primary damping function is shearing of the visco-elastic material24 which is enhanced by the mechanical keying of the ribs 20, 22 intothe material 24.

In FIG. 5, the ribs 20, 22 each extend approximately half way across thevoid 19 and are spaced apart laterally. The visco-elastic material 24connects the free ends of the alternate opposite ribs 20, 22. In thisway, loading to one panel 16 is transmitted to the other panel 18 viathe ribs 20, 22, passing through the visco-elastic material 24.

In FIG. 6, the ribs 20, 22 each extend approximately 40% of the wayacross the void 19. The ribs 20, 22 are co-linear which leaves a space26 therebetween. The visco-elastic material 24 surrounds the ends of allof the ribs 20, 22 and connects them all together. Thus load applied toone rib 20 is passed by the visco-elastic material and spread to allother ribs 20, 22, simultaneously damping that load.

In FIG. 7, ribs 20 extend from one panel 16 only and extend about 80% ofthe distance across the void 19. The visco-elastic material 24 coats theother panel 18 and surrounds the free ends of the ribs 20.

In FIG. 8, the ribs 20, 22 extend obliquely from the panels 16, 18 forexample at a 60° angle, although other angles are possible. The ribs 20,22 interdentate and the visco-elastic material fills the void 19. Theribs 20, 22 may be inclined at the same or different angle to oneanother. The angle of inclination may change along the length of the ribto optimise the damping efficiency and load distribution.

In FIG. 9, the ribs 20, 22 interdentate, extending around three quartersof the way across the void 19. Each rib 20, 22 has a head formation 28formed by a cross member at the free end thereof. The visco-elasticmaterial is configured similar to that in FIG. 6. The head formations 28increase the surface area of the free ends to promote rib-visco-elasticmaterial interaction.

In the embodiments described with reference to FIGS. 4 to 7 and 9 thevisco-elastic material only partially fills the cavity/void 19 formedbetween panels 16 and 18. However, the cavity 19 may also besubstantially completely filled with visco-elastic material.

In FIG. 10, the ribs 20, 22 are similar to those in FIG. 9 with anenlarged head 28 rather than a cross piece. The visco-elastic materialfills the void 19. Alternatively, or additionally, the ribs 20,22 mayterminate in a plurality of fingers or fins which fan out from the freeend, as shown in FIG. 11 a. In a similar fashion, the fingers or finsmay branch off from the ribs 20,22 along their span, as shown in FIG. 11b. Alternatively, and as shown in FIG. 11 c the fingers/fins mayadditionally be provided with a waved profile. That is to say, thefingers/fins vary in distance from the panels 16,18 in a sinusoidal likepattern along the height of the panel. Such an arrangement stiffens theribs 20,22 and alters its vibration characteristic.

In FIG. 12, the ribs 20, 22 have an interdentating saw-toothconfiguration.

In FIG. 13, the ribs 20,22 have a “U” shaped cross-section.

It is envisaged that all of the embodiments described above could bemade by machining one or both panels to include the ribs and securingthe panels together in known fashion, then injecting the visco-elasticmaterial. Alternatively, the visco-elastic material can be arranged onone or both of the panels prior to securing the panels together.

Although in the embodiment of FIG. 1 the ribs are shown substantiallyacross the whole of the panel 16, 18, the ribs may be restricted tosignificant areas, for example where high strain levels are likely to beexperienced. Also, the ribs are shown to include a curve or bend andthey could be straight. The ribs could be arranged parallel with eachother.

An alternative blade is shown in section in FIG. 14. The blade issimilar to that shown in FIG. 1 and parts corresponding to parts inFIGS. 1-3 carry the same reference numerals.

In FIG. 14, the blade 10 is made from first and second panels 16, 18.Each panel 16, 18 has a respective series of ribs 20, 22 extendingtherefrom. The ribs 20, 22 comprise a split warren girder structure.

FIGS. 15 a-d illustrate the manufacturing process for making the blade10 in FIG. 14.

The first stage in the manufacturing procedure is to arrange the panels16, 18 together sandwiching a web membrane 30 therebetween. The webmembrane 30 will become the projections 20, 22 at the end of theprocess. The inner surfaces of the panels 16, 18 are locally treatedwith a release agent. For panels manufactured from titanium, the releaseagent may be Yttria. The release agent is indicated by the cross-hatchedportion 32 on the panel 18 in FIG. 15 a.

The package of first and second panels and web membrane is heated andcompressed to the extent that the membrane 30 begins to become attachedto the inner surfaces of the panels 16, 18 except in the area coated byYttria 32. The attachment of the membrane 30 to the panel 16, 18 iseffected by diffusion bonding of the material. It should be noted thatthe panels and the web membrane are generally all formed of the samematerial which is suitable for such diffusion bonding and super plasticformation, such as titanium.

After the initial process is complete, the web membrane 30 is connectedto the first panel 16 at a first point by means of a diffusion bond 34and to the second panel 18 at a second point spaced from the firstpoint, again a diffusion bond 34. The membrane is typically 1-2 mmthick.

The web membrane 30 is pre-scored either with a continuous scored lineor with a series of perforations through the material thereof. The scoreline 36 extends across the full width of the rib-to-be at a pointbetween sections of the web membrane 30 which have bonded to the firstand second panels 16-18.

The resulting sandwich construction from FIG. 15 a is then arranged in afirst die 38 (see FIG. 15 b). The sandwich construction is thensubjected to a conventional super plastic forming operation. The die 38and the sandwich construction is subjected to heating to a super plastictemperature for the material in question. Generally that is titanium andso the material is heated to approximately 850° Celsius, although othermaterials may be used. Then an inert gas is injected at high pressureinto the interior of the sandwich construction between the panels 16,18. At the elevated temperature the high pressure gas pushes the panels16, 18 apart stretching the section of the membrane 40 that is notbonded to either of the panels 16, 18 so as to form a web 40. Thesandwich construction is allowed to continue to extend by moving apartof the panels 16, 18 until the panel 16, 18 contacts the surface of theopposing die plates 42, 44 of the die 38.

That results in the blade subassembly 46 shown in FIG. 15 b. The bladesubassembly is then allowed to cool and is arranged in a second die 48.The second die 48 has opposing surfaces on die plates 50, 52 which areformed as a female die formation for the ultimate shape of the panels16, 18. The surfaces of die plates 50, 52 are spaced further apart thanthe surfaces of die plates 42, 44.

The subassembly 46 is then subject to a hot forming process in which,again, the die 48 and the subassembly 46 is heated to a hot formingtemperature, for titanium normally around 750° Celsius. The inert gas isthen re-injected into the interior of the subassembly 46 at highpressure (30 bar). This causes the panels 16, 18 to be deformed and moveaway from each other against the surfaces of the die plates 50, 52.However, because the titanium is not at a superplastic temperature andbecause of the inherent weakness introduced by the score line 36, theweb 40 fails across its entire width along the score line 36 so as toform the first and second ribs 20, 22 extending from the first andsecond panels respectively.

The internal pressure is applied until the panels 16, 18 have assumedtheir final shapes. The fan blade 10 is then removed from the die andcooled. Subsequently, the internal cavity is chemically cleaned and avisco-elastic material 24 is injected into the blade 10 by means of aninjector 54, as shown in FIG. 15 d. That results in a fan blade 10 asshown in FIG. 14 filled with visco-elastic material and having a splitwarren girder structure so as to define ribs 20, 22 extending fromopposite panels 16, 18 into the void 19 therebetween.

FIG. 16 is a sectional view through a component, such as a fan blade 10.Parts corresponding to parts in FIGS. 1-14 carry the same referencenumerals.

The blade 10 comprises first and second panels 16, 18 spaced apart fromeach other with short ribs 20, 22 extending, respectively, from thepanels 16, 18 into a void 19 defined between the panel 16. Avisco-elastic material (not shown) can be injected into the void 19between the panels. The short ribs 20, 22 act as a mechanical key toincrease the effective damping capability of the visco-elastic materialwhereby the material does not rely on a bond or frictional interactionbetween the panel 16, 18 and itself but rather a mechanical interaction.

The shorter projections 20, 22 are formed in a similar fashion to themechanism described in FIGS. 15 a and 15 b above except the regionstreated with the release material are arranged so that no connecting webbetween the panels 16, 18 is formed in the superplastic formationprocess. Instead, the membrane is diffusion bonded to the panels to formthe protrusions.

In FIG. 17, a web membrane 30 is shown. The web membrane is generallymade from the same material as the first and second panels, oftentitanium is used. The membrane 30 is 1 mm-2 mm in thickness and it canbe seen that in the FIG. 18 arrangement parts of the membrane 30 havebeen cutaway to produce a rib pattern 60. It is envisaged that a varietyof rib patterns could be providing by cutting the web membrane 30 intodesired patterns. Additionally, the surface of the membrane 30 could becoated in selected regions with a release substance, such a Yttria.

As with the arrangement shown in FIG. 15 a, the membrane 30 is bonded tothe panels 16,18 in selected regions. However, since the membrane 30 hasalternate ribs 60 which are attached to the panel 16 and panel 18, thereis no material with which to form the a web 40, and hence the ribs 20,22are formed from the material of the membrane 30 bonded to the panels16,18. This is presented in FIG. 18, where ribs 22 are shown with adiffusion bond 34 connecting them to the panel 18.

In an alternative embodiment, and as shown in FIGS. 19 a and b, amachined protuberance is provided on the eventual outer surface of oneof the panels 16, 18. The protuberance 56 can be arranged at a pointcoincident with part of the web membrane arranged on the opposite faceor could be arranged at a different point. During the superplasticforming process, the protuberance 56 is pushed against the surface ofthe die plate. This causes the protuberance to be flattened against thedie plate and the material from the protuberance is forced in to createan inwardly extending protuberance 58 (see FIG. 19 b). If the outwardlyextending protuberance 56 is arranged coincident with the membrane 30,the resulting rib will comprise the membrane 30 and the inwardlyextending protuberance 58.

The internal ribs can be devised of any shape tolerated by a diffusionbonding process or can be manufactured by machining the internal skin ofthe blade panel.

The ribs could be made of pure metallic alloy or a composite. The joinbetween the internal wall of the panel and the internal ribs preferablyhas a leading chamfer to reduce local stresses in the area of thediffusion bond. As previously, the section of the blade covered in ribscan be localised or across the surface of the panels.

The ribs formed by the above process provide a mechanical key for betterinteraction between the blade panels 16, 18 and a visco-elastic dampingmaterial injected into the void 19 between the panels 16, 18. The ribshelp prevent delamination of the damping media from the inner surfaceand increase the surface area for the material to bond to.

The size, shape and position of the ribs can be selected to influenceany problematic vibration so as to move them outside of the normalrunning range of, for instance, the fan or blisk.

Although we have described the application of the above invention to afan blade, it is envisaged that any suitable hollow structure could usethe present invention.

1. A method of manufacturing an aerofoil for a gas turbine enginecomprising the steps of providing first and second panels, providing aweb between the first and second panels, deforming the panels and theweb by applying internal pressure between the panels so as to form aseries of internal cavities partitioned by the web, the method beingcharacterised by the steps of either cutting the web across its entirewidth or causing the web to fail across its entire width so as to definean aerofoil having first and second panels with at least one protrusionextending from the first panel partially across the space between thefirst and second panels.
 2. A method of manufacturing an aerofoilaccording to claim 1 in which the step of providing a web comprises thestep of providing a plurality of webs, locally weakening the webs acrosstheir entire width at a position in the webs spaced from the endsthereof, disposing the plurality of webs between two panels, causing thewebs to be joined to the panels, deforming the panels and the webs intwo stages, the first stage comprising the steps of heating the panelsand the webs to a superplastic temperature range and applying aninternal pressure between the panels so that the panels are pushed apartto contact a die in a first die position, the second stage comprisingthe steps of maintaining the panels and the webs at a hot formingtemperature range, below the superplastic temperature range, andapplying an internal pressure between the panels so that the panels arepushed apart to contact a die in a second die position, whereby thelocally weakened parts of the webs fail across the entire width thereof.